This section provides background information related to the present disclosure which is not necessarily prior art.
Many double ended power conversion topologies employ either a center tapped primary with two low sided switches (connected to the neutral/earth) or a single primary with power switches configured in half bridge (2 transistors drive) or full bridge (4 transistors drive) configuration. However, all of these circuits employ full wave rectification on the secondary side. If the output voltage is high, then bridge rectification is provided with only a single secondary winding. However, for converters which have low output voltage but high output current, bridge rectification results in higher conduction losses. Accordingly, a center tapped full wave rectifier is used due to lower conduction losses in only one rectifier during each half cycle. To keep the voltage spikes and losses lower, the transformer is designed to have a low leakage inductance.
A prior art half bridge push-pull converter system 100 that operates in a continuous conduction mode is illustrated in FIG. 1. FIG. 3 illustrates a topology used in the construction of prior art center tapped transformers operating in continuous conduction mode converters as illustrated in FIG. 1. The primary winding of a transformer is split into two parts represented by Np1 and Np2 and the two secondary windings represented by Ns1 and Ns2 are sandwiched between the two parts of the primary winding Np1 and Np2. This construction offers a good coupling between each secondary and primary while the two secondary windings Ns1 and Ns2 are coupled to each other as well to keep commutation period after dead time or “duty cycle loss” as low as possible. Some times, the two secondary windings also use bi-filar winding technique to improve their coupling.
Another power conversion topology 200 used in prior art is illustrated in FIG. 2. The system 200 is a prior art LLC resonant converter that operates in a discontinuous conduction mode. FIG. 4 illustrates a topology used in prior art to reduce coupling between the two secondary windings of the center tapped transformer operating in a discontinuous conduction mode as illustrated in FIG. 2. In this construction, the primary winding is sandwiched between two secondary windings. Although the two secondary windings are decoupled from each other to a large extent, the non conducting secondary still experiences the current field created by the primary winding adjacent to it. Thus the proximity losses due to eddy current still exist.
Various techniques have been used to provide a practical and cost effective transformer construction that offers a tight and equal coupling of each secondary winding with the primary winding to reduce the winding proximity losses.